A magnesium alloy is used for automobile parts and household appliances as an alloy for die casting or a castable alloy.
Alloys put to these uses are magnesium-aluminum alloys such as an AZ91 alloy (Mg, 9.0%-Al, 0.7%-Zn, 0.2%-Mn) and an AM60 alloy (Mg, 6.0%-Al, 0.2% Mn).
As a quality control method for such magnesium alloys, there has been a demand for the bath analysis method that can be performed easily, rapidly and safely at the site of casting.
For example, the bath analysis technique which utilizes the shape of a cooling curve during solidification has been established and has found widespread use for cast iron, aluminum alloys and zinc alloy castings.
However, such an established technology has not been proposed for magnesium alloys.
Furthermore, magnesium alloys pose problems such that molten magnesium is easily flammable, and its accurate cooling curve is difficult to obtain.
A magnesium alloy is utilized as a die castable alloy for precision parts. In this case, slight changes in the composition of the alloy are known to cause great changes in the yield.
A magnesium alloy may be used after remelting. During this remelting, changes in the components of the alloy occur.
As a result, a casting failure happens, or a trouble such as the lack of strength of the resulting casting occurs.
To solve these various problems, the establishment of a bath component analysis technique for a magnesium alloy has been desired.
In recent years, parts or cases for household appliances have been required to be smaller in wall thickness and more precise, and higher fluidity has been demanded for AZ91 alloy. AM60 alloy is used as a part required to have high impact strength among automobile parts. However, these alloys have a low aluminum content, and increase in melting point. Thus, unless the temperature of the molten metal is raised, appropriate fluidity is not obtained. However, the raise in the molten metal temperature causes the problem of the oxidation of the molten metal or the elution of the injection area.
To solve such problems, it is effective to 1 set the aluminum component at a high content to lower the melting point, or 2 improve fluidity, within the range of the components of AZ91 alloy or AM60 alloy. Delicate improvements and adjustments of the alloy composition that are associated with these measures cannot be satisfied by the alloy manufacturer requiring a mass production system as a prerequisite. Special manufacturing in a small quantity causes the problem of an increased cost.
A delicate change in the alloy composition on the part of the casting manufacturer involves the problems of requiring chemical analysis, taking time and entailing costs.
The objects of the present invention are to provide a bath analysis technique for a magnesium alloy (AZ91 alloy) which estimates the proportion of the aluminum component in the magnesium alloy by utilizing the shape of the cooling curve of the magnesium alloy during solidification; a component adjusting technique for the magnesium alloy; and a technique for correcting the aluminum component in the magnesium alloy with the aid of these techniques to produce the desired magnesium alloy.
Another object of the present invention is to provide a high fluidity magnesium alloy improved so as to have a higher aluminum component content than in conventional alloys, and a technique for producing such a magnesium alloy.